The inspiration regarding the construction of this compact unit was actually an impulse buy of a reincarnation of a magazine that I had fond memories of from my youth. I used to drive my mother to distraction with my accumulation of electronics magazines as it was a more commonplace and widespread hobby than it seems to be today. Almost everything was analogue, and if you wanted digital, you bought 74 series TTL logic integrated circuits. Personal computing was virtually unheard of, and I remember the huge occasion when the school science department were presented with two Apple II desktop computers.

Since I became involved in railway modelling, I have not forgotten my old hobby, and indeed my old employment, as I worked, initially in electronic manufacturing, then computer engineering, back in the days when you didn’t throw items away, but used a soldering iron to fix them, even at customer premises. I have always kept an eye out for articles in magazines and now on the internet, for items that relate to railway modelling, whether I am going to use them, or not.

I spotted an article in the October 2019 issue of Practical Electronics, so I bought the magazine. I wasn’t really into DCC at the time, but it was railway-related so that was that. Fast forward two years, and I now have two DCC control station set-ups, one using a Digikejis DR5000 (compatible with virtually everything else), and the other using a Pi-Sprog. I also have four DCC-equipped locomotives, with two more under construction, and one old one also to be equipped. By all accounts, it is getting serious, so when I found the magazine again, I thought the project would be useful for me and possibly appeal to a wider audience.

I won’t go into excessive detail on how it works, suffice it to say that there are two methods of powering the unit to get the required DCC track voltage (12-13V recommended); either using an MT3608 DC Boost Converter Module (USB powered) or an external power supply plugged into the microcontroller PCB. There is a jumper on the shield to allow you to change this as you require. The DCC signal is derived from a dual timer, the 556, which has been around for very long time and is capable of providing a 500kHz signal at 200mA. The board derives feedback by using a current-sense resistor, although the actual DCC signals with correct timing are derived from the Arduino and converted to the required voltage by the 556. If you would like to see in more detail how the unit actually works, I would advise you to buy the back issue as a PDF from https://www.electron publishing.com/cproduct/october-2019-back-issue/ (£4.50) which will also give you complete assembly and programming instructions. The particular article is six pages long, with an extra two explaining how DCC data works.

As well as the jumper that allows the user to alter the way the DCC power is derived, there are a number of other jumpers that allow alteration of the I/O pins on the Arduino board. This is useful as it is possible to build the board so additional shields can be stacked on top of this particular one. There may be a conflict in the allocation of I/O pins between boards although the program uses certain pins, which would also have to be changed within the program.

Apart from the MT3608, which comes pre-assembled, there are no component acquisition issues with regards construction. Everything is readily available from the usual suppliers. Components I didn’t have in stock already I bought from Rapid Electronics, and from Amazon. To keep the cost of building to an absolute minimum, I would recommend shopping around for components. For example, you only need one of most of the resistor types, whereas Rapid only supply in multiples of five for the 1W resistors, and 100 for the 0.4/0.6W types. I managed to get the MT3608 from Amazon, but they were sold in multiples of 6 (for £3.99); I could conceivably use the remainder for other things, though. As I mentioned earlier, construction is not particularly difficult. The PCB is supplied screen- printed, and it is merely a question of fitting components of the required value in the matching location on the board. The only items of real note are to ensure that devices that require a particular orientation are mounted correctly. It is important to check the resistor values, as the markings are all very similar, and also the orientation of the electrolytic capacitor, the diode, the 556, and the MT3608 if used. I can’t stress too much the requirement to check your work as you go along, solder joints especially, and if you use the MT3608, you need to leave the 556 off while you set the output voltage.

Provided construction has been carried out correctly, and you have mounted the shield on the Arduino board, you can tell if it woks by viewing the LEDs on the Arduino board. There are a green (power) and yellow (‘L’) LED that should be lit. If they don’t light, remove the shield, and try again; if they light with the shield removed, check your assembly of the shield.

• Double Sided PCB from Practical Electronics, Item 09107181 (https://www.electronpublishing.com/product/digital-command-control-programmer-for-decoders-with-stackable-headers-october-2019/)
• Rapid 19-0272, 19-0273, 19-0274 14 pin 2.54mm headers 2x 6 pin 2.54mm headers 1x 3 pin 2.54mm header
• Rapid 22-0545 – 36 way header, but MOQ is 20 I bought a kit from Amazon which contains all the necessary headers for the project.
• 4x Jumper shunts Rapid 22-3565 (also available from Amazon)
• 1x 2-way terminal block 5/5.08mm spacing Rapid 21- 0440
• Arduino Uno or Mega 2650 (about £11 on eBay for the Uno)
• 1x USB B lead (if it doesn’t come with the Arduino)
• 1x MT3608 2A Voltage booster (Amazon, eBay,etc.)
• 1x NE556 or 556 dual timer (shop around for this)
• 1x 14pin DIL socket (optional, but must be ‘turned pin’)
• 1x 1N5819 1A Schottky Diode Rapid 50-0305 (must be Schottky, 1N4001, etc. is not acceptable) MOQ-10
• 1x 100uF 25v electrolytic capacitor Rapid 11-2922 MOQ-5
• 1x 6.8Ω 1W Resistor Rapid 73-0056 MOQ-5
• 1x 2.2Ω 1W Resistor Rapid 73-0053 MOQ-5
• 1x 10kΩ 0.6w Resistor Rapid 62-3583 MOQ-100
• 1kΩ 0.6w Resistor Rapid 62-3564 MOQ-100
• 1x 100Ω 0.6w Resistor Rapid 62-3545 MOQ-100

Again, if you shop around, it should be possible to buy the resistors in the required quantity, although the unit price may be significantly higher.

For a more detailed feature on construction and programming, please view the associated ‘Guild Extra’ video, where I have tried to illustrate the magazine text, and provide a ‘how to’ guide with regards programming. The video is available at the following URL https://youtu.be/Zl5-LDH1fZE or via the ‘Guild Extra’ tab on the Gauge O Guild website.